rob@kaa.eng.ohio-state.edu (Rob Carriere) (07/11/88)
There have been several recent posting in this newsgroup to the effect that booting from a floppy is dangerous, that a HD might damage the data if started from an unparked state etc. I don't think so. Reason: It takes a digital circuit at most a couple of hundred microseconds to complete any power-up state races. In the case of the hard disk or a 5.25 floppy, the rw heads are removed from the media by means of a spring. This effect has to be overcome before anything can happen; this a mechanical phenomenon, it will take milliseconds. In the case of the 3.5 floppy, this device first has to slide open the door on the disk before it can even start to think about lowering the heads onto the media. If you listen during power-up, you will notice that there is a pause of about a second before the disk door slides open. In summary, by the time the rw heads get to the point where they could do damage, the control circuitry has long since settled down. If there are problems, this reflects either a design error in the hard_ and or software, or a transient glitch. Rob Carriere
neil@cs.hw.ac.uk (Neil Forsyth) (07/14/88)
In article <378@accelerator.eng.ohio-state.edu> rob@kaa.eng.ohio-state.edu (Rob Carriere) writes: >If you listen during power-up, you will notice >that there is a pause of about a second before the disk door slides >open. Not that it matters much to the discussion, but the noise you hear is not the disk door sliding open but the drive pin slipping into the funny shaped hole in the disk hub. If you look at a 'naked' drive with a disk in it you'll see the disk door is already open. _____________________________________________________________________________ / "I think all right thinking people in this country are sick and tired of \ ! being told that ordinary decent people are fed up in this country with ! ! being sick and tired. I'm certainly not and I'm sick and tired of being ! ! told that I am!" - Monty Python ! ! ! ! Neil Forsyth JANET: neil@uk.ac.hw.cs ! ! Dept. of Computer Science ARPA: neil@cs.hw.ac.uk ! ! Heriot-Watt University UUCP: ..!ukc!cs.hw.ac.uk!neil ! ! Edinburgh ! ! Scotland ! \_____________________________________________________________________________/
farren@gethen.UUCP (Michael J. Farren) (07/17/88)
rob@kaa.eng.ohio-state.edu (Rob Carriere) writes: >It takes a digital circuit at most a couple of hundred >microseconds to complete any power-up state races. This is true enough (usually), but if the design is bad, the result might be a state you do not want - such as read/write flipflops being in the "write" state. NOTE: I don't say this happens, and it would be pretty bad design if it did, but it IS possible. >hard disk or a 5.25 floppy, the rw heads are removed from the media by >means of a spring. This effect has to be overcome before anything can >happen; this a mechanical phenomenon, it will take milliseconds. In >the case of the 3.5 floppy, this device first has to slide open the >door on the disk before it can even start to think about lowering the >heads onto the media. If you listen during power-up, you will notice >that there is a pause of about a second before the disk door slides >open. Not on any 3.5" diskette drive I've ever seen. The shutter opens when you put the diskette into the drive. The mechanism is purely mechanical, and has nothing to do with the power. Similarly, a 5.25" drive might possibly have a solenoid to lift the heads when power is removed, but most drives either do not (the heads are in contact with the media whenever the disk is fully inserted and the lever thrown) or have had the solenoid disabled - the "clack-clack-clack" of the solenoid is generally enough to drive you batty real quickly. What sort of drives do you have, that you can hear this delay? >In summary, by the time the rw heads get to the point where they could >do damage, the control circuitry has long since settled down. If >there are problems, this reflects either a design error in the hard_ >and or software, or a transient glitch. Hmm. "Transient glitch". Like, the transient glitches that you get all through your system when the power comes up or goes down? You do as you will. I'll continue to take the diskettes out before I power up or down, thank you. -- Michael J. Farren | "INVESTIGATE your point of view, don't just {ucbvax, uunet, hoptoad}! | dogmatize it! Reflect on it and re-evaluate unisoft!gethen!farren | it. You may want to change your mind someday." gethen!farren@lll-winken.llnl.gov ----- Tom Reingold, from alt.flame